1. Field of the Invention
The present invention relates to a method and system for detecting whether the refrigerant charge level in an air conditioning system for a vehicle is low in a system utilizing on-board computer software and existing sensor inputs.
2. Background Art
Vehicle air conditioning systems circulate refrigerant through a closed-loop circulation system including a compressor, a heat exchanger and an expansion device. The performance of an air conditioning system degrades if the air conditioning system loses a significant portion of a refrigerant charge volume. If a significant portion of the refrigerant charge is lost, the air conditioning system may fail.
Loss of refrigerant reduces the amount of oil circulating in the system. If the loss of refrigerant is substantial, the compressor may be starved of oil which can lead to compressor failure. A loss of refrigerant can also cause the compressor to pull the air conditioning system into a vacuum which also starves the compressor of oil. If the compressor continues running in a starved condition, the compressor will eventually fail.
After compressor failure, it is expensive to replace the compressor and repair other damaged components of the air conditioning system. In contrast, if a loss of refrigerant is detected before damaging the compressor, the cost of repairing an air conditioning system that has a slow leak is a fraction of the cost of replacing a failed compressor. Most vehicle drivers are not able to determine whether an air conditioning system has a low charge until the air conditioner fails.
It has been proposed to add multiple pressure and temperature sensors throughout the air conditioning system to provide a low A/C charge detection system. However, the cost of adding additional pressure and temperature sensors in the air conditioning system is difficult to justify. There is a need for a low charge detection strategy that does not require adding pressure and temperature sensors throughout the air conditioning system. There is also a need for a low charge detection system that is capable of detecting a small loss of refrigerant before any damage is done to the compressor.
These and other problems are addressed by Applicants' system and method as summarized below.